99 Solara intermittent starting problems

Friend of mine has a 99 V6 Solara that has developed a starting problem in the last week or so. If the car has sit overnight or for a few hours it starts fine, but if the car is at operating temp and you cut it off and try to cut it back on in say 10-20 minutes the car will not start. Engine will turn over but will not start. Car runs fine the rest of the time. Wondering if anyone has seen or heard of this problem before. Thanks in advance for any help.